Historically, a gas metal arc welding apparatus consisted principally of a welding machine which provided a source of an electric current to an electrical welding circuit. One side of the circuit was connected to a clamp, preferably spring loaded, which held a consumable metal wire electrode and was adapted to be held by an operator and the other side of the circuit was connected to the work piece to be welded. The outer surface of the electrode was covered with a flux which emitted an inert gas to prevent oxidation in the welding zone during the welding process when the electrode was heated. In operation the operator held the clamp and struck an arc between the electrode and the work piece to initiate the welding process. When the electrode was consumed the operator had to discontinue the welding process and insert another electrode into the clamp.
More recently, welding guns have been developed for use by operators as substitutes for the clamps having consumable electrodes which must be replaced frequently. Wire feeders used in conjunction with the welding guns provide a continuous source of consumable steel wire electrode to the welding gun. The wire electrode may pass from the feeder to the gun through a Bowden wire contained in a conduit connected to the welding gun. The conduit also may have a tube for providing a source of pressurized inert gas to the welding gun, a conductor for providing a current source from a welding machine to the gun and one or more pairs of control wires. A typical welding gun may have a handle with a switch connected to one or more pairs of control wires to enable the operator to operate a welding machine, a wire feeder and a gas solenoid to thereby control the feed of a wire electrode and the flow of gas to a work piece. Normally such a welding gun has an adapter with a contact tip at the front end of the gun through which the wire electrode exits to the work piece. This contact tip further functions to conduct current supplied by a welding machine to the electrode as the wire is fed through it. In most instances different sizes of contact tips may be attached to an adapter in order to accommodate different sizes of wire electrode. A nozzle attached to the adapter directs inert gas to the welding site.
Typically, a conduit which connects a welding gun to an electric current generating welding machine, a source of inert gas and a wire feeder is constructed as a concentric cable assembly. This assembly may have a resilient central gas tube, a multiple strand current transfer wire wound around the outer surface of the gas tube and at least one pair of control wire conductors entwined within the current transfer wire. A Bowden wire assembly for the wire electrode may be positioned within the gas tube. A resilient outer sheath overlies the outer surface of the current transfer wire and functions as an insulator.
One disadvantage of prior art welding machines resides in the fact that they are not ergonomically designed. As an example, in some machines the cable assembly is connected to the welding gun in such a fashion that the electrical connection for the current transfer cable is located at the rear end of the gun. This design necessitates the use of a strain relief at this end of the gun. With a strain relief the weight of a conduit containing the cable coming up to the gun from a floor is cantilevered outwardly some distance from the rear end of the gun. This results in a downwardly acting force some distance from the end of the gun which acts to make the front end of the gun pivot upwardly in the hand of an operator. Thus, the operator constantly must exert a counter rotating force on the gun during the entire time it is in his hand.
Additionally, the traditional welding gun design best accommodates a work piece positioned such that the operator can work with the welding gun above the piece with the contact tip at the front end of the gun from which the welding electrode emanates pointed downwardly. If a work piece or surface to be welded requires the contact tip of the gun to be rotated to either side of a vertically downwardly orientation the operator must twist his wrist in order to grip the welding gun handle properly. It has been learned that operators who utilize welding guns over a long period of time tend to exhibit some degree of carpal tunnel syndrome in the joint of the wrist which holds the welding gun. It has been surmised that the syndrome arises as a result of the strain exerted on the operator's wrist as he acts to counterbalance the torque exerted on the gun by the cable coming up from the floor to the strain relief at the rear of the gun and by the strain exerted on the wrist when he must rotate his wrist to angle the contact tip at the front of the gun to different angular positions. Some welding guns are constructed such that a head tube which carries the adapter and contact tip may be rotated to position the contact tip at different angles with respect to the front of the gun. However, in order to rotate the contact tip the connection to a current transfer wire must be loosened, the contact tip assembly rotated and the electrical connection again re-established. Such a procedure requires the use of tools and is time-consuming and inconvenient.
An additional disadvantage of traditional welding guns relates to the mechanical connection of the concentric cable assembly to the gun. One type of connection for the attachment of the current conducting cable to a head tube at the front end of the gun which conducts current to the adapter and contact tip assembly utilizes a conical connector threadably attached to a locking cone nut. The conical connector/cone nut connector requires that the end of the outer sheath of the conduit be stripped and removed to expose the wound multiple strand current transfer wire. This wire must be distributed evenly around the outer surface of the conical connection. Additionally, the ends of the multiple strand wire must be trimmed to the proper length to ensure that they do not interfere with the threaded portion of the connector and cone nut. Thereafter, the locking cone nut must be screwed onto the conical connector such that the current transfer wire strands are squeezed between the outer surface of the conical connector and the inner surface of the cone nut. Inasmuch as the conical connector/cone nut assembly is constructed from metal components the assembly must be insulated carefully as it conducts substantial amounts of current during the welding operation. Making the connection of the current transfer wire to the head tube in this manner requires a substantial period of time.
Another type of connection for the attachment of the current conducting cable to a head tube utilizes a brass connecting lug. In this assembly the metal head tube is inserted into an opening in the brass connecting lug and the gas tube from the concentric cable assembly is fed directly into the head tube. The outer sheath is stripped from the cable assembly and the multiple strands of current transfer wire are twisted together to form a pigtail which is inserted into the opening in the brass connecting lug parallel to and beneath the head tube. A plurality of set screws are threaded into the connecting lug above the head tube to bias the metal head tube against the current transfer wire such that the wire pigtail is squeezed between the head tube and the inner wall of the connecting lug. Because the brass connecting lug is made out of metal the lug must be completely insulated and care taken to ensure that the operator's hand does not contact the lug. This connection utilizes an expensive metal lug and requires a substantial amount of time to make because of the preparation involved.
The welding gun of the present invention overcomes many of the disadvantages inherent in the design of traditional welding guns. This welding gun has an ergonomic design which positions the connection of the concentric cable assembly to the head tube at the front end of the gun. The mechanical connection of the concentric cable assembly is made in such a way that the outer sheath of the cable is not disturbed. In fact, the outer sheath assists in making the electrical connection. Additionally, non-conductive, non-metallic elements are utilized to attach the head tube which conducts current to an adapter/contact tip assembly to the multiple strand current transfer wire. This connection greatly reduces the likelihood that an operator's hand will contact any of the components within the welding gun which are electrically charged during the welding operation.
Additionally, the welding gun of the instant invention has a handle which overlies the connection of the multiple strand current transfer wire to the head tube. This causes the weight of the cable assembly between the floor and the rear of the gun to be balanced by the head tube and an adapter/contact tip assembly at the front of the gun. Consequently, the operator does not have to continuously counterbalance a large downwardly acting force at the rear end of the gun. Additionally, the design of the welding gun of the present invention allows the handle of the gun to pivot freely with respect to the head tube and the adapter/contact tip assembly. Rotation of the handle with respect to this assembly may be accomplished at any time by the operator without disturbing any electrical connection and without disassembling any of the components of the gun. Thus, an operator readily may position the adapter/contact tip assembly of the gun at any desired angle with respect to the handle to position optimally the contact tip while allowing his hand to remain in the most comfortable position.